Safety blasting cap



Aug. 23, 1927. 1,639,906

N. l. STEERS SAFETY BLASTING CAP Filed March 24; 1925 /Vf ske/1s,fnvenfor Patented Aug. 23, 1927.

UNITED STATES 1,639,966 PATENT oFFicE.

NEWTON I. STEERS, FlWILLIT'IIINGTON',l DELAWARE, ASSIGNOR T0 E. I. DUPONT DE NEMOURS & COMPANY, 0F WILMINGTON, DELAWARE, A COBIPOBATTON OFDELL- wann.

SAFETY BLASTING CAP.

Application mea umn 24, 1925. serial N6. 17,864.

This inventionis in the art of explosives and has particular relation toelectric blasting caps. As is of course well understood in the art, suchcaps comprise a suitable shell loaded with a sensitive and violentexplosive,- for example, ulminate of mercury, with suitable conductorsleading into the shell, and permanently connected therewith, forconducting an e ectric current to the charge to explode the same. Inuse, the cap is placed in close relation to the blastin charge of high"explosive to be detonate and the exploding of the cap gives the shockand heat necessary to cause detonation of the charge.

The leads of a cap are generally of considerable length, say ive or sixfeet. That is to say, they are so long that when the' .cap is carried inthe hand in theordinary way the exposed ends of the uncoiled leads arenot in the immediate control of the workman, and may come into contactwithy a chargedelectric conductor. It is a common practice for theworkman to uncoil the leads at semey lace distant from the point wherethe cap 1s to be used and then to carry the cap to that point, with itswires dragging along the ground. There are often stray currents in theground, or there are charged rails, or what not, and should the leadscome in contact therewith, thel cap may be exploded', resulting inserious accidents and, indeed, death. There are, of course, many othei`circumstances under which accidental explosion due to exposed leads mayoccur. I have devised a cap with its leads so arranged that dan ers ofthe type indicated vare eliminated. t is the major ob]ect of theinvention to provide such a cap. To this end, and also to improvegenerally upon devices of the character indicated, the inventionconsists in the various matters herein; after described and claimed.

.Without restricting the invention thereto, it is described withreference to the embodiment thereof illustrated in the accompanyingdrawing. In the drawing, Figure 1 is an elevational view of a cap withthe leads broken out to economize space, and Figure 2 is an enlargedfragmental plan view showing the manner in which the leads arepreferablyarran d in accordance with the 1nvvention. Re erring'nowto the drawingThe illustrated cap designated generally as 1, comprises the 2, o

any pIOPel 1113.-

lengths outside the shell; but at their free ends are, for a shortdistance, without insulation so that they may be readily connected withthe terminals of a current supplier, this, of course, being the usualpractice.

Now, in accordance with the present in# vention, the leads are shortedat their free ends as indicated at 7. With this arrangement, should theshorted ends come into connection with a current, the current will notpass down the leads to explode the char e. Preferably, the shorting isaccomplished y twisting the leads together, this being, I have found,much more satisfactory than interposing a brid e between the leads, bothfrom the point o View of `makin an inexpensive and thorough short androm the point of view of making a short which can be readily broken bythe workman when he desires to use the cap. With the illustratedconstruction, too, the exposed leads canbe readily shorted throughoutVtheir exposed portions, it only being necessary to closely twist theleads together throughout such ortions except for the short tips 4", 5b.T us, there is no unshorted length between the short 7 and theinsulation. Desirably, and as shown more particularly in Figure 2 at 8,the insulation is carried up a short distance beyond the short or,expressed somewhat differently, the twisting is carried along theinsulated portions. This makes doubly sure that there shall be nounshorted portion between the short 7 andl the insulation. In twistingthe leads, it is desirable that care be taken to twist them veryclosely, thereby to bring them into intimate close contact throughoutthe twisted length, thus to insure a hig ily effective short. When 'theworkman wishes 'to operatively connect the cap with a source of current,he merel has toy untwist the leads, thus destroyin t e short, thisoperation, of course, not eing done until the cap has been placed inposition for use.

With this arrangement, even thou h the workman does bring the exposedlea into tainer, said leads having uninsulated portions, with suchportionsv twisted together through a substantial lengththereof.

2. In a blasting cap, an 'explosive container, and electric leads fromsaid container, said leads having insulated and uninsulated portionswith the uninsulated portions twisted together through a substantiallength thereof, with the twisting extending along the insulatedportions,

In testimony whereof I aix my signature.

NEWTON I. STEERS.

